Different Distributions Consider the range of the data (the minimum point to the maximum point). If there is no mode, then the distribution is relatively.

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Presentation on theme: "Different Distributions Consider the range of the data (the minimum point to the maximum point). If there is no mode, then the distribution is relatively."— Presentation transcript:

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Different Distributions Consider the range of the data (the minimum point to the maximum point). If there is no mode, then the distribution is relatively uniform. If the mean, median, and mode are about equal, then the distribution is roughly “normal”. If the mean and median are not roughly equal, then the distribution is “skewed”.

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Normal Distributions Advantage: let us know quickly the mean and the spread of the data. Mean is the center of the distribution Standard Deviation:

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Quick illustration of standard deviation Here are 2 data sets: 3, 4, 10, 11 3, 4, 5, 8 If we look at them, we see that the second data set is much closer together than the first. We also see that the data are closer to the mean in the second data set. We use the term standard deviation to describe how close the data is to the mean.

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Example Graph a normal distribution with a mean of 5 and a standard deviation of 1. Compare to mean of 6 and standard deviation of 1. Compare to mean of 3 and a standard deviation of 1 Compare to a mean of 5 and a standard deviation of 2. Compare to a mean of 5 and a standard deviation of 0.5.

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Issues to consider Bias: the way the data was collected; the way the data is displayed to mislead Validity: Answers the question asked. Reliability: Get the same answers each time.

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Examples of bias Asking a sample of freshmen to learn college students’ preference of dorms. Asking only working mothers about childcare issues. Asking only men about marriage issues. Using categories/intervals that hide important information in displays

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Examples of poor validity Asking questions on the first exam that focus upon content from 302A to determine if students learned the material from Chapter 7. Asking questions about political party affiliation to determine likelihood of voting.

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Examples of poor reliability Are you pleased with your life right now? Select the best way to mislead in a display; vs. what is the most important concept in not misleading the reader with a display? On a scale of 1 - 10, how ready are you for a test next week?